The present invention relates generally to switch closure time in a vehicle, and more particularly, to an apparatus for measuring the closure time of a switch in a vehicle when the ignition switch of the vehicle is off.
There is a need in the automotive industry to measure the amount of time needed for switch closure when a vehicle ignition switch is turned off or the engine is not running. There must be very low current draw from the switch monitoring system to prevent excessive battery draw. Current draw must be within the ignition off current draw requirement of the vehicle. Switch cleansing current requirements to maintain contact integrity must also be satisfied. The monitoring must withstand the automotive voltage range of 6-24 volts on the battery line. The vehicular main power supply and the particular microprocessor of the vehicular control module cannot run for long periods of time after the ignition is off, otherwise the car""s battery would drain. There is a need to monitor this time for a period of six weeks.
Conventional methods in the auto industry for monitoring switch closure whether by mechanical or electronic means have had calibration concerns and excessive current draw on the existing battery of the vehicle. For example, there is a need in the automotive industry to determine whether the fuel system leaks. The closure time of a pressure switch which resides in the fuel system of the vehicle is thus monitored. However, autocalibration is not possible with present methods of closure time determination without excessive battery drain. Accordingly, there is a need for switch closure time monitoring with very little current drain to operate the time base and which switches off completely after the switch closure time has been captured.
A switch monitoring system that measures the closure time of a switch in a vehicle when the vehicle""s ignition switch is off. The switch monitoring system includes an oscillator circuit as a pan of an application specific integrated circuit (ASIC). It provides a reference signal that is divided down to a nominal {fraction (1/60)} Hz waveform, and then used as the clock source for a 16 bit counter. The counter is a portion of the vehicle shut down timer system which monitors an external switch and captures data for a microprocessor module of the particular vehicle system in question. The switch monitoring system is powered by a low power stand-by voltage source to provide very low current draw thus preventing excessive battery drain.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.